Lab 12: Cerebellum Flashcards
Input via the inferior cerebellar peduncle
- vestibular receptors
- body surface and muscle receptors
- inferior olivary nucleus
Input via the middle cerebellar peduncles
- widespread areas of the cerebral cortex, after a synapse in pontine nuclei
- Outflow reaches the upper motor neuron systems via the superior cerebellar peduncle
Outflow via the Superior Cerebellar Peduncle
- Cerebral cortex, especially the SMA, after a synapse in the thalamus
- the red nucleus
Outflow via the Inferior Cerebellar Peduncle
-fibers from the cerebellum travel to brainstem upper motor neurons (vestibular nuclei, reticular nuclei)
Overview of the Intrinsic connections of the Cerebellum
axons that enter the cerebellum as climbing fibers from inferior olivary nuclei or mossy fibers from all other input terminate in the:
- cerebellar cortex
- deep nuclei of the cerebellum
Impulse transmission within the cerebellar cortex includes:
- termination of climbing fibers on Purkinje cell dendrites and deep cerebellar nuclei
- termination of mossy fibers on granule cells and deep nuclei
- ascent of granule cell axons as parallel fibers in the molecular layer
- termination of parallel fibers on Purkinje cells
- descent of Purkinje cell axons to deep cerebellar nuclei
Gross Anatomy of the Cerebellum
- major regions: vermis (midline region) and hemispheres (lateral)
- foldings of cerebellar cortex: folia (elevations like gyri) and fissures (depressions like sulci)
Anterior Lobe of the cerebellum
- anterior to primary fissure
- hard to find except on sagittal surface
Posterior lobe of the cerebellum
Most of cerebellum posterior to the primary fissure
-includes:
Tonsil: part of the cerebellar hemisphere that extends close to the midline; can herniated through the foramen magnum as a result of increased intracranial pressure
Flocculonodular Lobe of the Cerebellum
Nodule (nodules): vermal part
Flocculus: hemispheric part; found laterally, near the VIIth and VIIIth cranial nerves and the lateral aperture or foramen of Luschka, indicated grossly by the presence of choroid plexus
Gross connections of the cerebellum with the brainstem
Superior cerebellar peduncle: cerebellum to midbrain
Middle Cerebellar peduncle: cerebellum to pons
Inferior cerebellar peduncle: cerebellum to medulla
VestibuloCerebellum
Flocculonodular lobe; important for balance and eye movements
Spinocerebellum
Vermis (median zone) and medial hemisphere (intermediate zone)
-important fort adjustments for smooth movement of proximal (median zone) and distal limb (paramedian zone)
Cerebrocerebellum
-lateral hemisphere or zone: involved in motor planning
Fastigial Nucleus
Adjacent to midline; receives fibers from vestibulocerebellum and vermis of the spinocerebellum
Interposed Nuclei
-receive fibers from the paramedian zone of the spinocerebellum
Dentate Nucleus
-most lateral, largest, wrinkled; receives fibers from the cerebrocerebellum
Molecular Layer
-contains stellate and basket cell bodies
Purkinje Layer
Contains single row of Purkinje cell bodies
Granule Cell Layer
Contains granule cell bodies
Input/Output of the Cerebellum via Inferior Cerebellar Peduncle
- vestibulonuclei: receives fibers from the fastigial nucleus and cortex of the vestibulocerebellum. Send fibers to the vestibulocerebellar cortex and fastigial nucleus (as do axons directly from the vestibular nerve). Influences LMNs via vestibulospinal tracts and vestibulo-ocular paths
- receptors: both deep (esp. muscle spindles) and superficial-send impulses via fibers that pass through the lateral area of the spinal cord and the brainstem to enter the cerebellum via the inferior cerebellar peduncle
- Inferior olivary nucleus: receive input from cerebral cortex, reticular formation and red nucleus. Send climbing (olivocerebellar) fibers to the contralateral cerebellum via the inferior cerebellar peduncle
- Reticular Formation: contains reticular nuclei that receive drivers from the fastigial nucleus and influence LMNs via the reticulospinal tract
Input to the cerebellum via the middle cerebellar peduncle
basis pedunculi (crus cerebri) of midbrain contains:
- corticopontine fibers: medial 2/5 and lateral 2/5 of peduncle; are fibers from the cerebral cortex en route to synapse on pontine nuclei of the basal pons. Pontine nuclei send fibers across the midline into the contralateral middle cerebellar peduncle.
- corticospinal and corticobulbar fibers: middle 1/5 of basis pedunculi
Middle cerebellar peduncle: a major INPUT system to the cerebellum from the cerebral cortex, after a synapse in the pontine nuclei; contains only pontocerebellar fibers
- pontine nuclei: a pale group of cells in the base of the pons that are involved in transmission of info from the cerebral cortex to the cerebellum. They: receive terminals of corticopontine fibers and send mossy fibers to the contralateral cerebellar cortex and deep nuclei via middle cerebellar peduncle
- pontocerebellar fibers: leave pontine nuclei and cross midline to enter the contralateral middle cerebellar peduncle and travel to the cerebellar cortex and deep nuclei
Outflow from cerebellum via superior cerebellar peduncle
Contain fibers from interposed and dentate nuclei of the cerebellum that travel to and terminate in the red nucleus as cerebellorubral fibers and the thalamus as cerebellothalamic fibers
Levels of the Superior Cerebellar Peduncle
Rostral pons: located medial to the lateral lemniscus
Pons/midbrain transition: the beginning of the decussation of the superior cerebellar peduncle
Caudal Midbrain: the decussation of the superior cerebellar peduncle
NOTE: the lateral lemniscus is peripheral to the superior cerebellar peduncles in the rostral pons and terminates in the inferior colliculus. At the level of the inferior colliculus and caudal midbrain, the superior cerebellar peduncles travel centrally and decussate and are covered laterally by the general sensory paths (ALS, medial lemniscus, VTTT)
Red Nucleus
-receive cerebellorubral fibers from contralateral cerebellum; magnocellular part receives fibers from interposed nuclei and forms the rubrospinal tract
Cerebellothalamic Fibers
-fibers from the dentate and interposed nuclei that travel lateral to the red nucleus en route to ventral lateral nucleus (VL) of thalamus
From the thalamus, fibers ascend in the posterior limb of the internal capsule to reach primary motor and premotor cortices
Clinical Tests for Cerebellum
- Walking a straight line (a test for Gait ataxia)
- Heel-to-shin test (a test for lower limb ataxia in the absence of antigravity function)
- Finger to nose test (a test for a synergy of movement and intention tremor)
- Rapid alternating movements (to show dysdiadochokinesia)
- Stretch reflex (to show hypotonia)
- Have eyeballs follow finger (to test for eyeball oscillation or nystagmus)
